This invention relates to a technique for controlling copying of multimedia data composed of a video signal, an audio signal and so forth, and more particularly to a data processing apparatus wherein a decoder for decoding an electronic watermark (digital watermark) for copy control is built in an encoder for coding a video signal and/or an audio signal in order to protect the video signal and/or the audio signal against alteration.
Prevention of illegal copying or alteration of music or acoustic data (hereinafter referred to as audio signal) recorded on a CD (compact disc), prevention of illegal copying or alteration of a video signal (image signal) and an audio signal recorded on a DVD (digital video disc), prevention of illegal use or alteration of multimedia data transmitted over a digital broadcasting network and other protection of the copyright of multimedia data have been attempted from various points of view.
From the point of view of protection of the copyright, various attempts have been made to prevent illegal copying of literary works of multimedia data such as, for example, an image signal (or video signal) and an audio signal. It is to be noted that such information may sometimes be hereinafter referred to as contents.
FIG. 1 shows a concept of a system which carries out a copy control method.
Referring to FIG. 1, in order to effect copy control, an apparatus (signaling section) 110 on the source side signals copy control information together with contents (information) into a signal transmission path 120 so as to be transmitted to a recording apparatus 130 on the reception side. The signal transmission path 120 may take various forms such as broadcasting, package media and network distribution. A copy control information detection circuit 134 of the reception side recording apparatus 130 detects the copy control information from the contents transmitted thereto and produces a recording operation control signal representative of whether or not recording is permitted. A recording processing circuit 132 records the received contents onto a recording medium such as, for example, a CD only when the recording operation control signal indicates permission of recording. Naturally, if the recording operation control signal indicates inhibition of recording, the recording processing circuit 132 does not perform a recording operation onto the recording medium.
However, while the recording operation control signal originally indicates inhibition of recording (inhibition of copying), if it is altered so that it indicates permission of recording (permission of copying), then a recording operation onto the recording medium is performed by the recording processing circuit 132. Therefore, such alteration of the recording operation control signal must be prevented. Now, a method of such prevention is described.
FIG. 2 illustrates an example of copy control information for a digital audio signal.
Referring to FIG. 2, the copy control signal for a digital audio signal includes a bit representative of presence or absence of copyright, a generation bit and a category bit in a digital interface illustrated in FIG. 2 in accordance with the provisions of the SCMS (Serial Copy Management System). The copy control signal is multiplexed into contents of a signal addition section 112 of the source side apparatus 110, in this instance, into a digital audio signal, and transmitted over the signal transmission path 120 to the reception side recording apparatus 130 such as, for example, a DAT (Digital Audio Tape) recording apparatus or an MD (Mini Disc: trademark) recording apparatus. Then, the copy control signal is detected by the copy control information detection circuit 134 of the reception side recording apparatus 130 and used to control recording of the recording processing circuit 132.
An example of copy control information for a video signal is illustrated in FIGS. 3A and 3B.
Referring to FIGS. 3A and 3B, CGMS (Copy Generation Management System) bits are multiplexed into contents, in this instance, into a video signal, by the signal addition section 112 of the source side apparatus 110 within a VBI (vertical blanking interval) and transmitted to the signal transmission path 120. Then, the CGMS bits are detected by the copy control information detection circuit 134 of the reception side recording apparatus 130 such as a DVD recording apparatus and used to control recording processing of the recording processing circuit 132.
The SCMS bits for an audio signal and the CGMS bits for a video signal described above are laid open as formats for transmission systems and can be acquired readily by a third party. Therefore, there is the possibility that, although a copy control signal or a recording operation control signal indicates inhibition of copying, it may be altered so as to indicate permission of copying.
As a countermeasure for overcoming the problem just described, several methods which provide augmented security have been proposed. One of the proposed methods employs a SDS (Secure Digital Bus) system, and another one of the methods adopts an electronic watermark.
FIG. 4 shows a system which employs a SDS system.
Referring to FIG. 4, in the SDS (Secure Digital Bus) system, an authentication-key exchange section 144 of a transmission side apparatus 140 exchanges information of a key and so forth with an authentication-key exchange section 164 of a reception section 160, which is the other party of communication, over a signal transmission section 150 which has an IEEE (Institute of Electrical and Electronics Engineers) 1394 digital interface. The transmission side apparatus 140 side authenticates whether or not a decryption section 162 which is the other party of communication has a copy control function legally. Then, only if the other party has a legal copy control function, original contents S0 are encrypted by an encryption section 142 and transmitted to the reception section 160 over the signal transmission section 150. The original contents S0 in this instance may be one or both of a video signal and an audio signal or multimedia data.
In the SDB system, even if the signal transmission section 150 tries to alter a signal on the digital interface, this is impossible if a third party who tries to illegally use the transmission signal cannot decrypt the signal. Accordingly, the SDB system is considered to be an information transmission system which is high in security in a transmission path.
The electronic watermark (digital watermark, digital data embedding, or digital data hiding) technique embeds some information into contents so that the contents may have the information in a hidden state. When an electronic watermark is embedded into contents, for example, into a video signal, the electronic watermark is embedded into the video signal in such a form that it cannot be perceived (visually observed) readily by the eyes of a human being while the video signal itself is maintained. When an electronic watermark is embedded into an audio signal, it is embedded in such a form that it cannot be perceived readily by the sense of hearing of a human being while the audio signal itself is maintained.
It has been proposed to combine such an electronic watermark technique as described above with an illegal copying prevention technique for digital literary works (for example, xe2x80x9cThe xe2x80x98Electronic Watermarkxe2x80x99 Protects the Multimedia Agexe2x80x9d, Nikkei Electronics, Feb. 24, 1997, pp.99-124).
Various methods have been proposed to embed electronic watermark information into digital multimedia data. An exemplary one of the methods is described.
FIGS. 5A, 5B and 5C illustrate an example of an electronic watermark for an audio signal.
According to the electronic watermark technique, the following processing is performed. First, frequency components of the audio signal are analyzed to select those frequency components f1, f2, f3 and f4 (indicated by slanting lines in FIG. 5A) whose deletion has a comparatively little influence on the audio signal. Then, the selected frequency components are deleted once (blank portions of FIG. 5B corresponding to the slanting line portions of FIG. 5A). Further, into each of the deleted frequency components, a signal which has a level higher than a predetermined level indicating the value xe2x80x9c1xe2x80x9d and exhibits a certain degree of continuity to signal levels of adjacent signals or another signal which has a level lower than another predetermined level indicating the value xe2x80x9c0xe2x80x9d and exhibits a certain degree of continuity to signal levels of adjacent signals is inserted (as a replaced signal) as seen in FIG. 5C.
Various methods of embedding an electronic watermark into contents have been proposed in addition to the method described above. For example, an electronic watermark can be embedded not only into an audio signal as described above but also into a video signal.
Subject of the SDB System
A problem provided by the SDB (Secure Digital Bus) system illustrated in FIG. 4 is described below with reference to a system construction shown in FIG. 6.
In the SDB system shown in FIG. 4, the signal transmission section 150 surely has a high degree of security against stealing of a transmission signal and alteration of the transmission signal. However, the reception section 160 has some problem.
As seen from FIG. 6, after the authentication-key exchange section 164 performs authentication by exchange of a key with the authentication-key exchange section 144 of the transmission side apparatus 140 side, the decryption section 162 receives encrypted information and decrypts it. When the decryption section 162 decrypts the encrypted information, also the copy control information is decrypted together with the encrypted contents. A signal compression section 166 compresses the decrypted contents, for example, an audio signal. A recording signal processing circuit 170 records the compressed audio signal, for example, onto a CD or an MD. In this instance, in order to control operation of the recording signal processing circuit 170, a host computer 180 produces a control signal based on the copy control information decoded by the decryption section 162. In particular, the host computer 180 produces a control signal for inhibiting operation of the recording signal processing circuit 170 when the copy control information indicates inhibition of copying, but produces another control signal for permitting recording by the recording signal processing circuit 170 when the copy control information indicates permission of copying. When the recording signal processing circuit 170 records the compressed audio signal onto a CD or an MD, the operation thereof is controlled in accordance with the control signal.
However, in a path A along which the copy control information decoded by the decryption section 162 is signaled to the host computer 180, although the copy control information indicates inhibition of copying, there is the possibility that the copy control information may be stolen and altered so as to indicate permission of copying.
Accordingly, also in the SDB system wherein authentication processing is performed using a key and contents are encrypted and transmitted to assure the security of transmission of the signal transmission section 150, there is the possibility that the reception side apparatus may not maintain the security and copy control information or the like may be altered.
Subject Where an Electronic Watermark is Used
A construction and processing of a reception side apparatus where an electronic watermark is embedded in contents are described with reference to FIG. 7.
Contents such as, for example, an audio signal in which an electronic watermark is embedded are compressed by a signal compression section 202 of a reception side apparatus 200 and recorded onto a recording medium such as a CD or an MD by a recording signal processing circuit 206. Upon such recording, the electronic watermark is detected by an electronic watermark detection circuit 204 from the contents transmitted from the transmission side (source side) apparatus and having the electronic watermark embedded therein. The electronic watermark detection circuit 204 produces copy control information representative of inhibition or permission of copying in response to the detected value. The method of detecting an electronic watermark by the electronic watermark detection circuit 204 can be determined depending upon the method used to embed the electronic watermark on the transmission side.
The copy control information produced by the electronic watermark detection circuit 204 is signaled to a host computer 208. The host computer 208 produces a control signal for controlling operation of the recording signal processing circuit 206 from the copy control information and applies the control signal to the recording signal processing circuit 206. The recording signal processing circuit 206 performs a recording operation only when the control signal indicates permission of a recording operation.
Also in this instance, there is the possibility that, in the path along which the copy control information is transmitted from the electronic watermark detection circuit 204 to the host computer 208, the copy control information may be stolen and altered.
Common Subject
The problem common to both of the apparatus described above is that, to whichever degree the security is raised by embedding of an electronic watermark or encryption on the transmission side or the security in the transmission path is raised by performing authentication and key exchanging processing, the possibility is still high that copy control information may be stolen or altered readily on the reception side.
A countermeasure or specifications effective to raise the security in secrecy of information in a transmission path between different apparatus on the reception side have not been proposed till now.
It is an object of the present invention to provide a data processing apparatus and a data processing method which inhibits illegal accessing from the outside and prevents alteration of information.
In order to attain the object described above, according to an aspect of the present invention, there is provided a data processing apparatus for processing data in which additional data is embedded, comprising coding means for coding the data, detection means for detecting the additional data from the data, processing means for processing the coded data coded by the coding means, and control means for controlling operation of the processing means in response to the additional data detected by the detection means, the coding means controlling an output thereof in response to the additional data detected by the detection means, accessing to the additional data used to control the coding means being inhibited.